The artist painted lots of heads, mostly contorted, often screaming. Often the heads of popes, especially after Velazquez's Portrait of Pope Innocent X.
I used to hate, hate, hate Francis Bacon, his work so disturbed me; worse than Munch's The Scream which is also very mouth-centric. Now. What? I love Bacon? No. More nuanced. It speaks to me. Chronic facial pain. TMJD. Arthritis in the jaw. The words that are a horror. But just words. It's nice to find a painting because a picture is worth a thousand words.